modern_browser

Directive assigns which version of the browser is to be considered as modern.
As browser you can assign the values msie, gecko (Mozilla-based browsers) opera, safari, konqueror.

Of versions it is possible to assign in size X, X.X, X.X.X, or X.X.X.X. maximum values for each of their sizes respectively - 4000, 4000.99, 4000.99.99, and 4000.99.99.99.

Special value "unlisted" indicates to consider modern browser, not described by the modern_browser and ancient_browser directives.
If the headers do not contain "User-agent", the browser is considered ancient (unless "modern_browser unlisted" is specified).